PROJECT SUMMARY/ABSTRACT Pulmonary arterial hypertension (PAH) is a severe disease of the pulmonary vasculature characterized by high symptom burden, significant healthcare utilization, and poor survival. Recently developed targeted therapies have improved outcomes for patients with PAH; however, the disease remains significantly underrecognized and undertreated when patients are managed outside of PAH referral centers. Despite the importance of early diagnosis and initiation of treatment in altering the disease trajectory, little is known about the influences on PAH care on a population level including potential patient-, environment-, or system-level determinants of treatment for PAH. Single-center studies suggest that disparities in PAH outcomes may exist among different racial/ethnic or socioeconomic status groups, though the factors that account for these differences such as disparities in treatment rates among these populations remain to be determined. Expanding our understanding of PAH care beyond PAH registry data and single-center cohort studies is essential to close care gaps on a population level. Administrative data that captures care within a national, diverse, integrated health system such as the Veteran?s Health Administration (VA) can serve as an important tool to improve our understanding of the delivery of PAH care in usual community practice and to detect health disparities in PAH. To capitalize on this rich data resource for this purpose, we must first establish sound mechanisms to identify PAH in administrative data, mechanisms that are currently lacking in this field. I propose two foundational steps to enhance our understanding of the drivers of PAH care delivery in the community and to fill currently unmet needs in PAH research: 1) create and validate algorithms to differentiate PAH from other, more common forms of pulmonary hypertension in administrative data and 2) identify patient- and facility-level determinants of treatment for PAH. Completion of this research proposal will advance the field of PAH by generating a collection of validated tools that other PAH researchers can utilize to better address diverse research questions and by revealing drivers of PAH care delivery on a population level including racial/ethnic and economic disparities in treatment rates. The results of this study will establish a foundation on which to build and implement effective strategies to improve treatment rates and mitigate health disparities for patients with PAH. Meanwhile, the skills I gain through this mentored research project and complementary didactic training will advance my career goal of becoming a leading independent investigator focused on identifying and addressing cardiopulmonary health disparities.